A mysterious chemical spilled a year ago in Johnstown, Pa. Its vapor burned the eyes -- and led to fears of terrorism. To find out what the chemical was, firefighters turned to a Web service set up a month earlier by the Homeland Security Dept. Dubbed the Disaster Management Interoperability Services system, it helps responders in 300 communities trade data like lightning.

In Johnstown, Fire Chief Michael H. Huss logged on to the system and continuously updated six hospitals on victims' symptoms. Ultimately, he learned that the chemical was tear gas. Without the network, "we would have to place phone calls," says Huss. "Translate that six times, and the message gets changed six times." In less than two hours, all 40 victims were recovering and firefighters traced the leak to a careless former U.S. soldier.